The goal of our proposed research is the development of vaccines against Brucella infection that are safe and efficacious. Our general approach has focused on the use of live attenuated vaccines (LAV). The use of live attenuated organisms are generally considered to be the vaccine of choice for intracellular bacteria such as Brucella spp. This strategy take advantage of the natural properties of the organism, including cell invasion and tissue tropism while presenting a full complement of immunogens, and is supported by a history of success. However, currently available vaccines are unsafe for use in humans. We have sought to identify improved live, attenuated vaccine candidates that are safe for use in humans. Routine testing of potential Brucella vaccines utilizes the mouse model to evaluate virulence and immune protection. However, mice fail to exhibit the outward signs of Brucella infection. As a result the next step in evaluation of vaccine candidates has been in the target species. For human vaccine development this might suggest the use of nonhuman primates at this stage of evaluation. However, evaluation of vaccines may be performed in a small ruminant model such as sheep or goats to eliminate candidates that produce symptoms associated with disease including abortion, providing an ultimate evaluation of safety. Although placental tissue tropism remains a well-documented phenomenon in ruminants, Brucella has not been considered to be a significant cause of human abortion. However, recent evidence revealed a strong correlation between exposure and elevated rates of abortion in endemic regions. Furthermore, there is strong evidence supporting growth of Brucella melitensis in human trophoblasts. Taken together, these data provide strong support for continued development of our LAV based on the obvious need for improved protection strategies to reduce the potential for human disease. Experiments in sheep are expected to provide the support for experimentation to test these candidates in nonhuman primates with the ultimate goal of developing a Brucella vaccine that is safe and efficacious for human use. The efforts outlined have taken advantage of our recently developed platform (encapsulation) to prolong immune system stimulation without prolonging the survival of the vaccine strain. Using this innovative approach we have progressed through multiple levels of investigation to demonstrate efficacy and safety of the LAV providing strong justification to bring development to fruition. The competitive advantages and innovations of approach presented include: (1) evaluation of highly attenuated, safe, gene knockouts in well-established, stable genetic background; (2) safety evaluation under the most stringent conditions possible, (3) support for development of a nonhuman primate model; (4) potential to reduce biocontainment level and support for manufacturing (GMP) and future progress for clinical trials, production and distribution.